Field of the Invention
The present invention relates to an apparatus for producing multiple width, fiber tow strips, namely in particular, multiple width filter tow strips consisting of interlaced filaments, a method for producing these fiber strips, and an apparatus for carrying out this method.
By a filter tow strip is to be understood a fiber strip which is composed of interlaced filaments or fibers. The filaments of the filter tow strip being similar to a non-woven fabric or web consist for example of cellulose acetate. The filter tow strip is crimped or curled by a so-called crimping machine or curling device (stuffer box) and is then compressed to a bale, to be ready for further processing to cigarette filters for rod-shaped smoking articles. The entire manufacture from the starting product cellulose to the filter tow strip packed in the bale is known e.g. from "Die Herstellung von Rhodia Filter Tow" Technische Information 1-01, Rhone-Poulenc Rhodia AG, Freiburg, January 1993. The known filter tow strips show uniform interlacing of the filaments over the entire width of the strip and have a substantially constant weight over their length.
The U.S. Pat. No. 3,512,230 granted to Ettore Luzzatto describes generally a method and apparatus for the production of non-woven fabrics with interlaced and crimped filaments or fibers. A plurality of filaments is produced by a conventional extruder comprising a spinneret whose nozzles are in alignment and closely spaced apart so that the filaments of this plurality are closely adjoining to one another. This close side-by-side relationship among the several filaments, which lie in a single plane, could, however, be obtained in the not immediate neighborhood of the spinneret output end but somewhat distant therefrom.
The plurality of filaments, wherein the filaments retain this condition of coplanarity, parallelism and side-by-side relationship, is sent into and through a mechanical crimping device, wherefrom the plurality emerges at a given speed and in a crimped condition. The filaments under these conditions could exhibit physically ascertainable undulations or even a mere tendency towards assuming an undulate trend. In view of the side-by-side relationship among the individual filaments, the crimping effect sets up a number of points of localized contact among adjacent filaments, even assuming that many points of contact might have possibly been given rise to upstream of the crimping device.
The formation of these points of contact or interlacing of the filaments, where the individual filaments adhere and are initially being interlocked has, obviously, a mere casual nature on a microscopical scale and is regular only from a statistical point of view. As a matter of fact in view of the regular relative arrangement of the filaments of the plurality at the input of the crimping device, and also on account of the regular way in which the conventional device mechanically acts upon filaments and yarns being fed therethrough, it has been ascertained that the points of contact are distributed, with a surprisingly advantageous statistical distribution, on the plane containing the plurality of crimped filaments. These points of contact are prevailingly formed in that the filaments which, at the output of the crimping device are undulated in planes perpendicular to the plane of the plurality, and which are parallel and susceptible of being closely approached to one another, do not stay physically in said closely approached planes and, by being displaced, they come into mutual contact.
In order that the most favourable conditions for the formation of numerous regularly distributed points of contact may be achieved, it is advantageous that the known crimping device impart to the individual filaments undulations having an amplitude which is considerably wider than the interspace between closely adjoining filaments present in the plurality of filaments at the input end of the device.
In the DE 1 435 438 filed by Eastman Kodak Company in 1963 a method for introducing a continuous strip of cellulose acetate filaments into a crimping apparatus is described, which produces a tow from which cigarette filters could be produced. The known crimping apparatus (stuffer box) comprises a pair of transport rolls for catching the strip and for squeezing the strip of filaments therebetween in order to achieve an interlaced structure of the filaments of the strip, and a crimping chamber with a clapper gate unit for crimping the strip output of the pair of transport rolls by intermittent upsetting or compressing the strip.
The patent U.S. Pat. No. 4,259,769 to Greve et al. describes a method and apparatus for banding tows of filamentary material. Greve states that the known pneumatic banding devices are incapable of reliably converting the tow into a layer of uniform thickness, width and density because the accumulations of filaments in certain strip-shaped portions of the running tow are not spread apart in the same way as the thinner strip-shaped portions of the tow. Streams of air which pass through the tow flatten and increase the width of the tow, but their equalizing or homogenizing action is far from uniform. The object in the Greve's patent is to provide a method of banding a running tow of filamentary material in such a way that the width of the banded tow is more uniform and the orientation of filaments in the banded tow is more satisfactory than in known tows.
Greve's method consists of the steps of transporting the tow lengthwise to the nip of two advancing rolls along an elongated path and in a predetermined direction, directing a plurality of discrete streams of pressurized gaseous fluid, for instance transversely against the running tow so that each stream contacts and expands laterally a discrete strip-shaped portion of the tow, monitoring the permeability of such strip-shaped portions of the running tow, and adjusting the expanding action of the respective streams when the monitored permeability, that is the density of the strip-shaped portions deviates from a predetermined optimum value. The tow which consists of filamentary filter material is transported in a lengthwise direction by means of two rollers. The filaments of the tow are normally crimped and are movable relative to each other. The width of the running tow normally varies from increment to increment or at irregular intervals. Since the number of filaments in the tow is normally constant, the thickness and density of neighbouring strip-shaped portions of the untreated tow vary from portion to portion. The strip-shaped portions extend lengthwise of the tow i.e., in substantial parallelism with the marginal portions of the tow, and each strip-shaped portion is caused to move past a discrete banding device. Greve's apparatus comprises six neighbouring banding devices which respectively comprise plenum chambers forming a tow which extends transversely of the lengthwise direction and adjacent to a selected portion of the elongated path for the tow. The upper walls of the plenum chambers are adjacent to the underside of the running tow and are respectively provided with pairs of orifices which discharge streams of air against the strip-shaped portions of the tow. The streams expand the strip-shaped portions laterally and equalize the distribution of filaments so that the tow is converted into a wide layer in which the orientation of filaments is substantially uniform and the density of each laterally expanded strip-shaped portion matches or closely approaches a predetermined optimum value. Consequently Greve describes a monowidth fiber strip, that is the known tow having only one part.
The patent document U.S. Pat. No. 4,285,650 issued to Muller et al, describes an apparatus for producing tobacco product filter rods. Muller uses a paper web which has a multiplicity of rib-like deformations, which run parallel in the longitudinal direction, in the direction of movement, and are of a denser fibre structure, and also longitudinal zones, located between the former zones, having a highly fibrillated structure and a multiplicity of unconnected longitudinal grooves. The paper web is first fed to equipment which essentially consists of two embossing rollers which are arranged with their axes parallel and with the distance between the axes being adjustable. The two rollers have projecting ribs on their surfaces respectively, these ribs extending around the entire surface of the rollers and running parallel to the axes of the rollers. The two rollers have a cross-section with projecting ribs that are absolutely identical and the rollers are driven together in such a way that they rotate at the same surface speed.
The document GB 2 265 298 A, published on Sep. 29, 1993 describes a method of and a machine for making filters for rod-shaped smokers'products. Two or more tows of fibrous filter material are simultaneously advanced along neighbouring paths through several processing units into a rod forming unit to be converted into filter rods which are ready to be subdivided into filter rod sections of unit length or multiple unit length. At least one of the processing units is designed to simultaneously treat all of the tows, and at least one of these units is designed to treat the tows independently of each other, such independent treatment renders it possible to eliminate differences between the characteristics of the ultimate products or to intentionally impart to products obtained from different rods different characteristics such as density and/or the resistance to the flow of tobacco smoke. The plural tows can be withdrawn from a single source storing a discrete bale for each tow, a common bale for several tows or a bale having an integral tow of multiple unit width which is subdivided by separating means into several narrower tows not later than at the time of entering the unit or units which are designed to individually treat each tow on its way toward the rod forming unit. The tows can be advanced side-by-side in a common plane or in several planes above each other.
When using one integral tow of multiple width the separation into several narrower tows does provide quite strong fluctuations of the denier or titer of the narrower tows. These fluctuations affecting the quality, especially the pressure drop and weight, of the produced filter rods are difficult to avoid by the known apparatus.